1. Field of the Invention
The invention relates to polymeric resin based enclosed water systems comprising biocidal metal-ions preventing the formation of biofilm. The enclosed water systems commonly include reservoirs and/or delivery tubing having intermittent or continuous flow. Such water systems are most commonly used in the dental and medical fields.
2. Background of the Invention
The formation of sessile bacteria on water-bearing surfaces results in communities of live biofilms. Biofilms are implicated in a significant amount of human bacterial infections. Bacterial biofilms also cause fouling, product contamination, equipment failure, and decreased productivity due to downtime for system cleaning and replacement. Biofilms also cause fouling of the water that passes through the system and results in high levels of suspended, free-swimming (planktonic) bacteria. Planktonic bacterial cells alight on a surface, arrange themselves in clusters and attach. The collected cells begin producing a gooey matrix. The cells signal one another to multiply and form a microcolony. Chemical gradients arise and promote the coexistence of diverse species and metabolic states. Some cells return to their planktonic form and escape, forming new biofilms.
Conventional methods of killing bacteria (such as antibiotics, and chemical disinfection) are often ineffective with biofilm bacteria. The huge doses of antimicrobials required to rid systems of biofilm bacteria are undesirable environmentally (and perhaps not allowed by environmental regulations) and impractical medically (since what it would take to kill the biofilm bacteria would also potentially harm the patient). Standard chemical disinfectants and antibiotics often fail to eliminate biofilms because they do not penetrate biofilms fully or do not harm bacteria of all species and metabolic states in the films. Furthermore, typical biocides kill the bacteria by damaging the cell wall structure. This often results in the release of more toxic endotoxins.
In particular, biofilms present an ever-growing concern due to their prevalence in dental unit water systems. These systems provide particularly well-suited conditions for biofilm formation. The tubing has a very narrow bore (⅛ to 1/16-inch), providing a high internal surface-area-to-volume ratio. Low water pressure, low flow rates, and frequent periods of stagnation also encourage any bacteria introduced from the public water supply or saliva retraction to accumulate within the tubing. Numerous studies conducted over the past thirty years have identified the presence of waterborne opportunistic pathogens in dental unit water. For these reasons, the American Dental Association (ADA) and Centers for Disease Control and Prevention (CDC) have established guidelines for delivery of dental water with less than 500 colony-forming units (CFU) of heterotrophic bacteria per milliliter of water. In response to the need to abate this problem, many products have been developed, generally falling into one of four categories: independent water systems, chemical treatment methods, point-of-use filters, or sterile water delivery systems. Despite the available the aforementioned products, most of the systems available yield only marginal results.
Current approaches to improve the quality of water, and particularly, dental water include waterline flushing, independent reservoirs filled with distilled water, chemical “shock treatment”, continuous chemical treatment, mechanical filtration and automated in-line treatment devices. Waterline flushing may temporarily reduce bacteria levels however the biofilm remains completely active and at any given time a person may be exposed to elevated levels of bacteria. Independent water reservoirs filled with distilled water may begin free of bacteria, however without a residual disinfectant the water is readily contaminated from the biofilm within the reservoir and/or tubing. Mechanical filtration may be temporarily effective at filtering bacteria, however, problems with breakthrough, time and costs of replacement are prohibitive. In dentistry, “shock treatments” utilizing solutions with bleach, peroxide, or chlorhexidine have been administered, but the “shock treatments” must be repeated weekly and often daily because the biofilm actually begins to regrow in that short period of time. This type of system also requires use of only sterile water to slow down the biofilm formation. Mature biofilms are notoriously resistant to chemical disinfection including these “shock treatments”. Thus, if a practitioner does not treat his system for several weeks, the biofilm will become resistant to this method.
U.S. Pat. No. 5,158,454 incorporates an automated in-line ozone generator that is effective at continuous disinfection. The disadvantage of this device and similar others are that they are bulky and take up limited space from the operatory unit and are expensive to install and operate.
Another system utilized in controlling the presence of infectious microbes in water supplied to dental units is disclosed in U.S. Pat. No. 5,230,624. Here, an in-line filter is provided in a supply line leading to a dental instrument, such as a drill or the like, and contains a polyiodide purification resin. The resin functions to neutralize and kill bacteria by the release of iodine from the resin surface to the bacteria through a demand release process involving electrostatic attraction. The resin is positively charged such that the negatively charged microorganisms are attracted to the resin to the point where iodine is released directly into the microorganism. The disadvantage of the system is that the filters must be changed and the bacteria many times is not effectively controlled.
U.S. Pat. No. 6,106,771 describes a portable system and method for softening and disinfecting dental waterlines. Although period chemical treatment of water lines has been shown to provide temporary improvements in water quality, this approach has failed to provide continuous supply of bacteria free water.
Another system to control the presence of infectious microbes in water supplied to dental units is disclosed in U.S. Pat. No. 5,709,546. This invention provides a process by which mature biofilms, including biofilms of the type produced by gram negative bacteria such as pseudomonas aeruginosa, are reduced to the point of elimination through the use of a hydroxycarboxylic acid in relatively low concentrations so as not to be harmful to human tissue. Although the use hydroxycarboxylic acid in relatively low concentrations has been shown to provide temporary improvements in water quality, this approach has also failed to provide continuous supply of bacteria free water.
In light of the failure of the aforementioned techniques to control biofilm, a number of inventions have focused on developing antibacterial polymeric structures. U.S. Pat. Nos. 6,238,575 and 6,261,271 describe an enclosed fluid system structure conjugated with an organic antimicrobial agent as resistant to the formation of biofilm. Although test data indicates a zone of inhibition of bacteria growth, it does not demonstrate long-term resistance to biofilm formation. Biofilm resistance to organic antimicrobials and antibiotics are well documented. Furthermore, the leaching of toxic antimicrobials and antibiotics into the aqueous environment prohibits the use of the aforementioned inventions in potable water or medical/dental water applications.
Furthermore, silver, copper and zinc metal ion biocides have been developed and utilized as antimicrobial agents on and within many different substrates and surfaces. U.S. Pat. Nos. 4,933,178, 6,126,931, and 5,614,568 incorporate metal ion based biocides. Although these inventions present improvements to prior art, the practical application is inappropriate for sensitive end uses including potable, medical and dental water.
A need exists for a fluid handling system which resists the formation of biofilms. Ideally, the fluid handling system would be manufactured from a material which is capable of resisting the formation of biofilms when exposed to an aqueous environment. As a result, existing system designs and conventional component elements, such as tubing, containers, and receptacles could be utilized. In particular, only minimal changes to these systems would be required to replace non-biofilm resistance materials with biofilm resistant materials. Moreover, it would be beneficial to provide a biofilm resistant fluid handling system which requires minimum maintenance and is economically feasible.